The car has developed a cough/misfire at 3-4k rpm. It's only a recent development. The car idles fine and apart from a rather apparent water leak has no other major issues. 

 

So far I've changed:

 

Coil packs (a month ago)

MAF (a month ago)

N75 valve/relay (about 2 weeks ago)

Spark plugs (last night)

 

When I plug the code reader I have in I get:

 

P1296 Cooling system malfunction

P0418 SAI System control A circuit

 

Neither of which, according to a lengthy Google search, seem to be related to my problem.

 

It appears my problem is another "common issue these cars seem to come with. 

 

Any ideas after trying the usual fixes?

 

If your drive around with a known coolant leak then your asking for trouble. Remember the engine is aluminium, if you cook it (allow it to overheat),

then its game over , heat warping the cylinder head then needing a reskim etc.

The water could be leaking into one of the cylinders (if its not a hose), check the oil filler hole at the top for "mayo" on the inside of it,

if the water is mixiing with the engine oil you are risking  a major sieze up.

Or It could be coil pack wiring loom starting to fail.

 

1/ Fix water leak

2./Investigate, fix and clear error codes

 

See below for fault codes

http://wiki.ross-tech.com/wiki/index.php?title=Category:Fault_Codes&pagefrom=16503%2FP0119#mw-pages

 

http://wiki.ross-tech.com/wiki/index.php/17704/P1296/004758

Edited 25 September, 20178 yr by Silver Bullet

Which spark plugs did you use? I use NGK PFR6Q plugs in mine and haven't had any problems. On a previous car (Clio 172) I had a cough/loss of power at 5k rpm which went away after I replaced the cheap plugs with the correct NGK ones.

@ChubbyT - @vrsTom has sort of made a relevant point. You could have installed a new bad plug. If you still have the old set, get one of them, and fit it in place of each new plug in turn and see if that cures your misfire. (I knew a good pro mechanic who got caught out by this one)

54 minutes ago, KenONeill said:

@ChubbyT - @vrsTom has sort of made a relevant point. You could have installed a new bad plug. If you still have the old set, get one of them, and fit it in place of each new plug in turn and see if that cures your misfire. (I knew a good pro mechanic who got caught out by this one)

Only sort of? 

If the old plugs were past it and/or the wrong type then it could have been causing the issue. If one of the new plugs was faulty you'd expect the car to run worse than it was before - from my understanding of the OP he's replaced the spark plugs but the issue is the same as before. If the old plugs were the cause of the issue then replacing them with new plugs may not fix it if they're the wrong ones.

 

Few other questions for the OP:

Did you fit a genuine MAF? People on here have reported problems with non-genuine ones. Was the old MAF genuine? Have you tried running it with the MAF unplugged?

Which coil packs did you fit? What were the old coil packs?

Did you diagnose each of the parts you replaced as faulty - or were you trying to rule things out by replacing them?

 

As @Silver Bullet said - get the coolant loss fixed first.

Cheers guys. 

 

I'm not leaking coolant. I've replaced the coolant temp sensor and that's fixed that code.

 

I replaced the MAF with a pattern part. The other day I unplugged it just to check and the coughing seems to have stopped.

 

Hopefully if I relplace it with a genuine one it'll fix the issue.